The current invention is directed to a can, such as a metal can used to package carbonated beverages. More specifically, the current invention is directed to a can having an end with improved strength, and to an apparatus and method for making such a can.
Beverages, such as carbonated beverages, are typically packaged in cans made of metal, such as aluminum. Two piece cans are typically formed by seaming a can end to a can body. Traditionally, seaming is accomplished by forming a can end 10, shown in FIG. 1, in a die press. The can end 10 typically has a circular countersink bead 16, a substantially flat center panel 18, a seaming panel 13 that terminates in a peripheral curl 12, and a frustoconical side wall portion 14 that extends between the bead and the seaming panel. Traditionally, the side wall 14 is disposed at an angle A of about 14xc2x0 with respect to a line parallel to the centerline 7 of the can body 20. (Unless otherwise indicated, the numerical value of all angles referred to herein should be understood to be positive, meaning that the angle tapers away from the centerline of the can body as it extends upward in the direction from the bottom of the can body toward the can end. A negative angle is an angle that extends toward the centerline as it extends upward in the direction from the bottom of the can body toward the can end.)
Seaming is performed by disposing a flange 11 of the can body 20 under the seaming panel 13 on the can end 10. A seaming chuck 2 is then inserted into the can end 10, as shown in FIG. 1. Traditionally, seaming chucks 2 have frustoconical upper and lower wall portions 4 and 6, respectively. The lower wall portion 6 is typically disposed at an angle B that is a few degrees less than the angle A of the can end side wall 14 so that if the angle A of the can end side wall were about 14xc2x0, the angle B of the chuck lower wall would be about 11xc2x0. The upper wall portion 4, which typically has a length L of about 0.130 inch, is typically disposed at an angle C that is about 4xc2x0. Thus, the upper and lower wall portions 4 and 6 intersect at an edge 5 so as to form an obtuse angle of about 173xc2x0 (i.e., 180xc2x0+4xc2x0xe2x88x9211xc2x0). Typically, the edge 5 has a radius of curvature of about 0.005 inch. Since the angle B of the lower wall 6 of the chuck 2 is less than the angle A of the can end lower wall 14, a relatively large gap, which may be as much as 0.010 inch, is formed between the chuck side wall and the can end side wall in the vicinity of the chuck wall edge 5, as shown in FIG. 1.
Seaming is completed by sequentially applying first and second seaming rolls against the curl 12 so as to press the curl and the flange 11 against the upper chuck wall 4, thereby producing a standard double seam 22, shown in FIG. 2.
Unfortunately, although pressed against the chuck 2 during seaming, the side wall 14 of the can end tends to spring backxe2x80x94that is, radially outwardxe2x80x94when the pressure of the seaming roll is relieved. Thus, despite the fact that the upper and lower walls 4 and 6 of conventional seaming chucks 2 form two straight, frustoconical sections, the resulting side wall 14xe2x80x2 of the can end 10xe2x80x2 after seaming is arcuate, having a relatively large radius of curvature R1, as shown in FIG. 2. The curved nature of the seamed side wall 14xe2x80x2 weakens the strength of the seamed can end 10xe2x80x2.
Recently, a non-standard can end has been developed in which the side wall, after seaming, is formed by two straight sections intersecting at a circumferentially extending crease. Such a can end is shown in published PCT application WO 96/37414. This structure is achieved by initially forming the can end side wall at a large angle that is said to be preferably in the range of 40xc2x0 to 45xc2x0. According to the approach described in this published PCT application, the seaming chuck has a lower wall disposed at a similarly large angle and an upper wall disposed at an angle in the range of +4xc2x0 to 4xc2x0. While this approach results in a strengthened can end, unfortunately, the large can end side wall angle required in this approach precludes its application to standard can ends, in which the side wall angle is only about 14xc2x0, as previously discussed.
Consequently, it would be desirable to provide a method and apparatus for seaming a conventional end to a can such that the resulting seamed can end had a side wall of improved strength.
It is an object of the current invention to provide a method and apparatus for seaming a conventional end to a can such that the resulting seamed can end had a side wall of improved strength. This and other objects is accomplished in a method of seaming a can end to a can body comprising the steps of (i) forming a can end having a side wall and a seaming panel, the side wall formed by a single substantially straight section disposed at an angle with respect to the central axis that is within the range of about 12xc2x0 to 15xc2x0, (ii) inserting a chuck into the can end adjacent the side wall, the chuck having upper and lower portions forming upper and lower chuck walls, the lower chuck wall being substantially frustoconical and disposed at an angle with respect to the central axis that is no less than the angle at which the substantially straight section of the can end side wall is disposed with respect to the central axis, the upper chuck wall disposed at an angle with respect to the central axis that is within the range of about 0xc2x0 to xe2x88x922xc2x0, and (iii) seaming the seaming panel of the can end to a can body so as to reshape the can end side wall into upper and lower substantially straight sections, the upper and lower substantially straight sections intersecting at an obtuse angle.
The current invention also encompasses a chuck for use in seaming a can end to a can body, comprising (i) an upper portion forming an upper wall, the upper wall being disposed at an angle with respect to the central axis that is within the range of about 0xc2x0 to xe2x88x922xc2x0, and (ii) a lower portion forming a lower wall, the lower wall being substantially frustoconical and disposed at an angle with respect to the upper wall that is within the range of about 162xc2x0 to 168xc2x0.
The current invention also encompasses a seamed can comprising (i) a can body defining a central axis thereof, and (ii) a can end seamed to the can body, the can end having a side wall formed by upper and lower substantially straight sections, the lower substantially straight section disposed at an angle with respect to the central axis that is in the range of about 12xc2x0 to 15xc2x0, the upper and lower substantially straight sections intersecting at an obtuse angle so as to form a circular crease separating the upper and lower substantially straight sections.